Expandable stent and method for delivery of same

ABSTRACT

An expandable stent having a proximal end and a distal end in communication with one another, and a tubular wall disposed between the proximal end and the distal end. The tubular wall has a longitudinal axis and a porous surface defined by a plurality of intersecting members comprising a series of longitudinal struts disposed substantially parallel to the longitudinal axis of the stent. Each longitudinal strut in the series comprises flexure members for substantially complementary extension and compression of a diametrically opposed pair of the longitudinal struts upon flexure of the stent. The flexure members may comprise first and second curved sections which are of a different size. At least one of the curved sections may comprise an arc of greater than about 180°.

This application is a continuation of application Ser. No. 09/142,509,filed Feb. 18, 1999 (now U.S. Pat. No. 6,183,506, issued Feb. 6, 2001),which is a 371 of PCT/CA97/00152), filed Mar. 5, 1997 (designating theU.S.; and published in English as WO 97/32544 on Sep. 12, 1997), whichclaims benefit of (i) CA 2,171,047, filed Mar. 5, 1996, (ii) CA2,175,722, filed May 3, 1996, (iii) CA 2,185,740, filed Sep. 17, 1996,and (iv) CA 2,192,520, filed Dec. 10, 1996.

TECHNICAL FIELD

The present invention relates to an expandable stent.

BACKGROUND ART

Stents are generally known. Indeed, the term “stent” has been usedinterchangeably with terms such as “intraluminal vascular graft” and“expansible prosthesis”. As used throughout this specification the term“stent” is intended to have a broad meaning and encompasses anyexpandable prosthetic device for implantation in a body passageway (e.g.a lumen or artery).

In the past six to eight years, the use of stents has attracted anincreasing amount of attention due the potential of these devices to beused, in certain cases, as an alternative to surgery. Generally, a stentis used to obtain and maintain the patency of the body passageway whilemaintaining the integrity of the passageway. As used in thisspecification, the term “body passageway” is intended to have a broadmeaning and encompasses any duct (e.g. natural or iatrogenic) within thehuman body and can include a member selected from the group comprising:blood vessels, respiratory ducts, gastrointestinal ducts and the like.

Initial stents were self-expanding, spring-like devices which wereinserted in the body passageway in a contracted state. When released,the stent would automatically expand and increase to a final diameterdependent on the size of the stent and the elasticity of the bodypassageway. An example of such a stent is known in the art as theWallstent™.

The self-expanding stents were found by some investigators to bedeficient since, when deployed, they could place undue, permanent stresson the walls of the body passageway. Further, upon expansion, the stentwould shorten in length in an unpredictable fashion thereby reducing thereliability of the stent. This led to the development of various stentswhich were controllably expandable at the target body passageway so thatonly sufficient force to maintain the patency of the body passageway wasapplied in expanding the stent.

Generally, in these later systems, a stent, in association with aballoon, is delivered to the target area of the body passageway by acatheter system. Once the stent has been properly located (for example,for intravascular implantation the target area of the vessel can befilled with a contrast medium to facilitate visualization duringfluoroscopy), the balloon is expanded thereby expanding the stent byplastic deformation so that the latter is urged in place against thebody passageway. As indicated above, the amount of force applied is atleast that necessary to maintain the patency of the body passageway. Atthis point, the balloon is deflated and withdrawn within the catheter,and subsequently removed. Ideally, the stent will remain in place andmaintain the target area of the body passageway substantially free ofblockage (or narrowing).

A stent which has gained some notoriety in the art is known as thePalmaz-Schatz™ Balloon Expandable Stent (hereinafter referred to as “thePalmaz-Schatz stent”). This stent is discussed in a number of patentsincluding U.S. Pat. Nos. 4,733,665, 4,739,762, 5,102,417 and 5,316,023,the contents of each of which are hereby incorporated by reference.

Another stent which has gained some notoriety in the art is known as theGianturco-Roubin Flex-Stent™ (hereinafter referred to as “theGianturco-Roubin stent”). This stent is discussed in a number ofpatents, including U.S. Pat. Nos. 4,800,882, 4,907,336 and 5,041,126,the contents of each of which are hereby incorporated by reference.

Other types of stents are disclosed in the following patents:

U.S. Pat. No. 5,035,706 (Gianturco et al.),

U.S. Pat. No. 5,037,392 (Hillstead),

U.S. Pat. No. 5,147,385 (Beck et al.),

U.S. Pat. No. 5,282,824 (Gianturco),

Canadian patent 1,239,755 (Wallsten), and

Canadian patent 1,245,527 (Gianturco et al.),

the contents of each of which are hereby incorporated by reference.

While these prior art stents have achieved a varying degree of success,the art is constantly in need of new stents having improved flexibilityand stability while being able to be readily implanted with little or notrauma to the target lumen.

In our Canadian patent application number 2,134,997 (Penn et al.), thecontents of which are hereby incorporated by reference, there isdescribed an improved expandable stent. The stent comprises a tubularwall disposed between the proximal end and the distal end. The tubularwall has a longitudinal axis and a porous surface defined by a pluralityintersecting members arranged to define a first repeating pattern. Thefirst repeating pattern comprises a polygon having a pair of side wallssubstantially parallel to the longitudinal axis. A first concave-shapedwall and a second convex-shaped wall connect the side walls. The firstwall and the second wall are equidistant along an axis which is parallelto the longitudinal axis. The stent is expandable from a first,contracted position to a second, expanded position upon the applicationof a radially outward force exerted on the stent.

As disclosed in the '997 application, the first repeating pattern can beimplemented in, inter alia, a mono-tubular expandable stent and abifurcated expandable stent.

While the stent disclosed in the '997 application is an advance in theart, in certain cases, a significant force is required to achieveexpansion in the target body passageway. Further, implantation of thestent disclosed in the '997 application can be difficult in certainsituations where the unexpanded stent must travel through asignificantly curved pathway to the target body passageway.

Accordingly, it would be desirable to have an improved stent whichovercomes these disadvantages. It would be further desirable if theimproved stent could be readily adapted, inter alia, to mono-tubularexpandable stents and bifurcated expandable stents. The latter type ofstents would be useful in treating aneurysms, blockages and otherailments. It would also be desirable if such a stent was relatively easyto implant. It would be further desirable if such a stent were capableof being uniformly expanded at relatively low pressure while obviatingor mitigating longitudinal shrinkage thereof. It would be furtherdesirable if such a stent were not susceptible to asymmetric internalcoverage of the body passageway, a problem associated with “coil”-typestents—see, for example, U.S. Pat. No. 5,282,824 (Gianturco). It wouldbe further desirable if such a stent was not susceptible to movementalong the longitudinal axis of the body passageway during or afterimplantation. It would be further desirable if such a stent wascharacterized by a desirable balance of lateral flexibility in theunexpanded state and radial rigidity in the expanded state.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a novel expandablestent which obviates or mitigates at least one of the above-mentioneddisadvantages of the prior art.

Accordingly, in one of its aspects, the present invention provides anexpandable stent comprising a proximal end and a distal end incommunication with one another, a tubular wall disposed between theproximal end and the distal end, the tubular wall having a longitudinalaxis and a porous surface defined by a plurality of intersecting memberscomprising a series of longitudinal struts disposed substantiallyparallel to the longitudinal axis of the stent, each of the longitudinalstruts comprising flexure means for substantially complementaryextension and compression of a diametrically opposed pair of thelongitudinal struts upon flexure of the stent, the stent beingexpandable from a first, contracted position to a second, expandedposition upon the application of a radially outward force on the stent.

Thus, in this aspect of the present invention, we have now discoveredthat the use of flexure means in the series of longitudinal struts leadsto a very desirable balance of lateral flexibility of the unexpandedstent and radial rigidity of the expanded stent. Practically, theflexure means confers lateral flexibility to the unexpanded stent byallowing diametrically opposed pairs of the longitudinal struts toundergo substantially complementary extension and compression. If oneconsiders a stent in a flexed state, a first longitudinal strut disposedat the tangent of the bend (i.e. in two dimensions) will expand inresponse to the bending moment. In contrast, a second longitudinal strutdisposed diametrically opposite (this can mean above, below or in thesame radial plane as) the first longitudinal strut will compress inresponse to the bending bend moment. Generally, the degree of extensionand compression will be substantially complementary. In other words, inmost cases, the first longitudinal strut will expand and lengthen afirst distance and the second longitudinal strut will compress andshorten a second distance. Preferably, the first distance is greaterthan the second distance and most preferably, the sum of the firstdistance and the second distance is substantially equal to the sum ofthe original lengths of the first longitudinal strut and the secondlongitudinal strut.

The specific shape of the flexure means disposed in the longitudinalstrut is not particularly restricted provided that it confers lateralflexibility to the unexpanded stent by allowing diametrically opposedpairs of the longitudinal struts to undergo substantially complementaryextension and compression. The term “diametrically opposed pairs of thelongitudinal struts”, as used in this specification, is intended to havea broad meaning. Thus, the “pair” can include opposed struts in the samehorizontal plane (i.e. the same ring of polygons) or in differenthorizontal planes (e.g. one strut in a first ring of polygons and theother diametrically opposed strut in a second ring of polygons above orbelow the first ring). Preferably, the flexure means comprises at leastone lateral section disposed in the longitudinal strut, more preferablyat least a first lateral section and a second lateral section disposedin the longitudinal strut. By “lateral section” is meant a section ofthe longitudinal strut which is bowed in or out of (i.e. radially from)the strut. The apex of the lateral section may be pointed, rounded orsubstantially flat. When the flexure means comprises a first lateralsection and a second lateral section, the two sections may be symmetricor asymmetric (in the case of asymmetric this includes two sections ofthe same shape but different size and two sections of different andsize). Further, when the flexure means comprises a first lateral sectionand a section lateral section, the sections may be bowed in the same oropposite direction.

A particularly preferred embodiment of the flexure means comprises asinusoidal or S-shaped section (various examples of such a section areillustrated herein and discussed below). Preferably, the sinusoidal orS-shaped section is adjacent the second apex of the polygon and theremaining portion of the strut is substantially straight. This featureimproves the lateral flexibility of the stent thereby facilitatingimplantation thereof and may further mitigate longitudinal shortening ofthe stent upon expansion.

In another preferred embodiment, at least one, more preferably both, ofthe side walls (i.e. longitudinal struts) of the polygon comprises thesinusoidal or S-shaped section. Preferably, the sinusoidal or S-shapedsection is disposed at an end of the side wall. This feature improvesthe lateral flexibility of the stent thereby facilitating implantationthereof and may further mitigate longitudinal shortening of the stentupon expansion.

When a sinusoidal or S-shaped portion is disposed in the side wallsand/or the strut connecting the first apex and the second apex (ifpresent), the precise shape of the portion is not particularlyrestricted and generally takes the form of an “S”. Thus, the sinusoidalor S-shaped portion may be comprised of a pair of joined curved sectionswherein each curved section has an arc of about 180°—i.e. this isillustrated in FIG. 8 of the present application. The term “arc” denotesthe angle from one end of the curved section to the other about theradical point of the curved section. Alternatively, the sinusoidal orS-shaped portion may be comprised of a pair of joined curved sectionswherein each curved section has an arc of greater than 180°—this isillustrated in FIG. 9 of the present application. Further the pair ofjoined curved sections can be of the same size (this is illustrated inFIGS. 8 and 9 of the present application) or of differing size (this isillustrated in FIG. 10 of the present application), the latter being themost preferred embodiment.

Preferably, the series of longitudinal struts containing the flexuremeans comprises all substantially longitudinal struts comprised in theplurality of intersecting members making up the porous surface of thestent.

Preferably, for this aspect of the present invention, the intersectingmembers are arranged to define a first repeating pattern comprised of apolygon having a pair of side walls substantially parallel to thelongitudinal axis (i.e. a pair of the above-mentioned longitudinalstruts comprising flexure means), a concave-shaped first wall having afirst apex and a convex-shaped second wall having a second apexconnecting the side walls. As used throughout this specification, theterms “concave-shaped” and “convex-shaped” are intended to have a broadmeaning and a shape having apex. Thus, the first wall has a first apexand the second wall has a second apex. Thus, the first apex (i.e. of theconcave-shaped first wall) is directed into the polygon whereas thesecond apex (i.e. of the convex-shaped second wall) is directed awayfrom the polygon.

In another of its aspects, the present invention provides an expandablestent comprising a proximal end and a distal end in communication withone another, a tubular wall disposed between the proximal end and thedistal end, the tubular wall having a longitudinal axis and a poroussurface defined by a plurality intersecting members arranged to define afirst repeating pattern comprised of a polygon having a pair of sidewalls substantially parallel to the longitudinal axis, a concave-shapedfirst wall having a first apex and a convex-shaped second wall having asecond apex, the first wall and the second wall connecting the sidewalls, at least one of the first apex and the second apex beingsubstantially flat, the stent being expandable from a first, contractedposition to a second, expanded position upon the application of aradially outward force on the stent.

In this aspect of the invention, it is has been discovered that the useof such a first repeating pattern (including at least one of the firstapex and second apex being substantially flat), with or without theflexure means present in the side walls of the polygon in the firstrepeating pattern, results in an improved stent. The advantagesassociated with the use of such a such a first repeating pattern includethe following:

1. the force required to expand the stent is substantially reduced;

2. the stent is subjected to less traumatic stress during expansion;

3. plastic deformation of the stent during expansion is facilitated;

4. construction of the stent is facilitated; and

5. upon expansion of the stent, warpage of the first apex and the secondapex is obviated or mitigated.

The provision of at least one of the first apex and the second apexbeing substantially flat usually results in the apex of theconcave-shaped first wall and/or the convex-shaped second wall having apair of shoulders. Preferably, these shoulders are rounded. Theprovision of such round shoulders results in the following additionaladvantages:

6. mitigation of potential trauma to the target body passageway from:(i) endoluminal contents within the passageway, and (ii) the contours ofthe passageway;

7. the resulting expanded stent is more stream-lined and flow-directedwhich mitigates potential trauma to the target body passageway;

8. further reduction in the force required to expand the stent;

9. an improved stent expansion ratio is achieved (i.e. ratio of expandedstent diameter at maximum expansion to unexpanded stent diameter);

10. upon expansion of the stent, the concave-shaped first wall and theconvex-shaped second wall are in a substantially orthogonal relationshipto the longitudinal axis thereby improving the rigidity of the stent(this is very important to mitigate the occurrence of stent recoil); and

11. the pattern of the expanded stent improves the rheology of fluidflow in the body passageway.

When the stent of the present invention includes the above-mentionedfirst repeating pattern, it is preferred to provide a connecting strutbetween the first apex and the second apex. Generally, the connectingstrut will be substantially longitudinal (i.e. it will be parallel tothe longitudinal axis of the stent). This feature mitigates lifting ofthe shoulders referred to above as the stent is flexed, for example,when passing the stent through a curved body passageway. The result ofthis is that potential trauma to the body passageway is mitigated sincescraping of the body passageway by the shoulders is mitigated.

In a preferred embodiment, the connecting strut is curved with respectto the longitudinal axis (this is described and illustratedhereinbelow). Preferably, the strut is sufficiently curved to have alength of up to about 35%, more preferably up to about 15%, even morepreferably in the range of from about 2% to about 8%, most preferably inthe range of from about 3% to about 7%, greater than the distancebetween the first apex and the second apex. This feature improves thelateral flexibility of the stent thereby facilitating implantationthereof. In some cases, the curvature may be designed to comprise theflexure means discussed above. In other words, the shape of thecurvature may be designed substantially complementary extension andcompression of the connecting strut upon flexure of the stent.

Yet another preferred feature of the stent of the present invention isthe provision of one or both of the side walls of the polygon of therepeating pattern being curved. Preferably, both side walls are curved.More preferably the curvature serves as flexure means as describedabove. Ideally, the curved side wall has length of up to about 35%, morepreferably up to about 15%, even more preferably in the range of fromabout 2% to about 8%, most preferably in the range of from about 3% toabout 7%, greater than the distance between the termini of theconcave-shaped first wall and the concave-shaped second wall. Thisfeature improves the lateral flexibility of the strut therebyfacilitating implantation thereof.

Preferably, both the strut and the side walls are curved. Morepreferably, each of the curved members are of substantially the samelength.

Yet another preferred feature of the stent of the present invention is,in addition to the strut and side walls of the polygon being curved, theprovision of all longitudinal walls of the polygon of the repeatingpattern being curved. Thus, in this embodiment of the invention, theconcave-shaped first wall comprises a pair of curved first apex wallsconnecting the first apex and the side walls of the polygon, and theconvex-shaped second wall comprises a pair of curved second apex wallsconnecting the second apex and the side walls of the polygon. Again, insome cases, the curvature may be designed to comprise the flexure meansdiscussed above. Ideally, the curved first apex walls and the curvedsecond apex walls each have a length of up to about 35%, more preferablyup to about 15%, even more preferably in the range of from about 2% toabout 8%, most preferably in the range of from about 3% to about 7%,greater than the straight (i.e. non-curved) distance between the firstapex and the side walls, and the second apex and the side walls,respectively. In this embodiment, it is further preferred to havesubstantially all adjacent curved walls in an annular section of therepeating pattern (i.e. of the struts, first apex wall, second apex walland side walls) are substantially equidistant from one another. Thispreferred feature of the stent of the present invention even furtherenhances the lateral flexibility of the stent thereby furtherfacilitating implantation thereof.

Yet another preferred feature of the stent of the present invention isprovision of a porous surface comprising multiple designs. Specifically,in certain cases, it may be desirable to design the stent to varyingdegrees of relative flexibility and rigidity along the length thereof.Thus, the relatively flexible portion(s) of such a stent wouldfacilitate delivery of the stent to a target body passageway through arelatively tortuous route, while the relatively rigid portion(s) of thestent serves facilitate maintaining the patency of the body passageway.As will be discussed in more detail hereinbelow, this may be achieved byvarying the repeating pattern design along the longitudinal length ofthe stent.

An aspect of the present invention relates to the provision of anexpandable bifurcated stent. As used throughout this specification, theterm “bifurcated stent” is intended to have a broad meaning andencompasses any stent having a primary passageway to which is connectedat least two secondary passageways. Thus, trifurcated stents areencompassed herein. Further, one of the secondary passageways can be acontinuation of the primary passageway with the result that the othersecondary passageway is essentially a side branch to the primarypassageway.

The stent of the present invention (bifurcated or mono-tubular) canfurther comprise coating material thereon. The coating material can bedisposed continuously or discontinuously on the surface of the stent.Further, the coating may be disposed on the interior and/or the exteriorsurface(s) of the stent. The coating material can be one or more of abiologically inert material (e.g. to reduce the thrombogenicity of thestent), a medicinal composition which leaches into the wall of the bodypassageway after implantation (e.g. to provide anticoagulant action, todeliver a pharmaceutical to the body passageway and the like) and thelike.

The stent is preferably provided with a biocompatible containing, inorder of minimize adverse interaction with the walls of the body vesseland/or with the liquid, usually blood, flowing through the vessel. Thecoating is preferably a polymeric material, which is generally providedby applying to the stent a solution or dispersion of preformed polymerin a solvent and removing the solvent. Non-polymeric coating materialmay alternatively be used. Suitable coating materials, for instancepolymers, may be polytetraflouroethylene or silicone rubbers, orpolyurethanes which are known to be biocompatible. Preferably howeverthe polymer has zwitterionic pendant groups, generally ammoniumphosphate ester groups, for instance phosphoryl choline groups oranalogues thereof. Examples of suitable polymers are described inInternational application number WO-A-93/16479 and WO-A-93/15775.Polymers described in those specifications are hemo-compatible as wellas generally biocompatible and, in addition, are lubricious. It isimportant to ensure that the surfaces of the stent are completely coatedin order to minimize unfavourable interactions, for instance with blood,which might lead to thrombosis.

This good coating can be achieved by suitable selection of coatingconditions, such as coating solution viscosity, coating technique and/orsolvent removal step.

In another embodiment of the invention, the stent may be joined to apolymer material. Specifically, a polymer material may be extruded ontothe stent in such a manner that it envelops at least a portion of thestent. This technique may be used to join two or more stents with aflexible polymeric tube. This technique may also be used to join a stentto another prosthetic device such as a tube, a graft and the like. Thus,in this embodiment of the invention, the stent is incorporated into anendoluminal prosthesis.

In yet another embodiment of the invention the stent may be secured(e.g. by suturing) to an existing endolurninal prosthesis such asGortex™ material or to biological material such as basilic vein. In thisregard, securing of the stent to the existing endoluminal prosthesis orbiological material may be facilitated by designing the stent such thatan end of the stent comprises an annular row of the above-mentionedpolygons is having a convex-shaped wall with a flat apex.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be described with reference tothe accompanying drawings wherein like numerals designate like parts andin which FIG. 1 illustrates an exploded perspective view of amono-tubular stent prior to expansion;

FIG. 1A illustrates an exploded view of a portion of the stentillustrated in FIG. 1;

FIGS. 2-10 each illustrate a two dimensional representation of variousembodiments (not to relative scale) of a repeating pattern useful in thestent of the present invention;

FIG. 11 illustrates an ostial stenosis to which a preferred embodimentof the invention may be applied; and

FIGS. 12a-12 i illustrate various embodiments of flexure means (in twodimensions) which may be disposed in the longitudinal struts ofpreferred embodiments of the present stent.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to FIG. 1, there is illustrated a stent 10. Stent 10comprises a proximal end 15 and a distal end 20. Stent further comprisesa tubular wall 25 disposed between proximal end 15 and distal end 20. Asillustrated, tubular wall 25 is porous. The porosity of tubular wall 25is defined by a plurality of intersecting members 30. Intersectingmembers 30 define a first repeating pattern designated A in FIG. 1.

As illustrated and with further reference to FIG. 1A, repeating patternA is a polygon comprising a pair of side walls 35,40. Side walls 35,40are substantially parallel to a longitudinal axis 45 of stent 10 andthus side walls 35,40 may be considered to be longitudinal struts(indeed with reference to each of the drawings, side walls may also beconsidered to be longitudinal struts). Side walls 35,40 are connected bya concave-shaped wall 50 and a convex-shaped wall 60.

As illustrated, concave-shaped wall 50 is made up of a trio of segments52,54,56. In the illustrated embodiment, segment 54 is the apex ofconcave-shaped wall 54. As is evident, segment 54 is a flat apex andresults in the provision of a pair of substantially square shoulders57,58. Convex-shaped wall 60 is made up of a trio of segments 62,64,66.In the illustrated embodiment, segment 64 is the apex of convex-shapedwall 60.

It will be appreciated by those of skill in the art that the provisionof first repeating pattern A, as illustrated, necessarily defines andprovides for a second repeating pattern B. It will also be appreciatedby those of skill in the art that second repeating pattern B is a mirrorimage of first repeating pattern A taken along an axis (not shown)substantially normal to longitudinal axis 45. Thus, in the illustratedembodiments, adjacent rows of repeating pattern A and repeating patternB may be considered to by interlocking polygons or “arrowheads”.

It will be further appreciated by those of skill in the art that theshape of concave-shaped wall 50 and/or convex-shaped wall 60 can bemodified without departing from the function and performance of thestent provided that at least one of concave-shaped wall 50 andconvex-shaped wall 60 retain a substantially flat apex. For example, thetrio of segments can be replaced by a suitably curved or arcuate wall.Alternatively, more than three segments can be used to defineconcave-shaped wall 50 and/or convex-shaped wall 60. Other modificationswill be apparent to those of skill in the art.

It will be further appreciated by those of skill in the art that variouswalls of first repeating pattern A and second repeating pattern B may beomitted (and even desired) at selected points along the body of thestent without departing from the spirit and scope of the invention. Forexample, it is possible to omit one or both of side walls 35 and 40 atselected points along the body of the stent with a view to improving thelongitudinal flexibility of the stent. Further, it is possible to omitone or more of segments 62,64,66 at selected points along the body ofthe stent with a view to improving the lateral flexibility of the stent.

Still further, the stent depicted in FIG. 1 can be modified to omit, ona selected basis, first repeating pattern A and/or second repeating Bwith a view to improve flexibility of the stent and to allow access toother structures (e.g. side branches/arteries) outside the bounds of thestent.

With reference to FIGS. 2-10, there are illustrated a number ofpreferred embodiments of repeating pattern A. For the sake of clarity,numerals in FIGS. 2-8 have the same final two digits as thecorresponding numerals in FIG. 1. Thus, for example, the concave-shapedwall is depicted as element 50 in FIG. 1, element 150 in FIG. 2, element250 in FIG. 3, etc.

Thus, as illustrated in FIG. 2, repeating pattern A is comprised of aconcave-shaped wall 150 and a convex-shaped wall 160, the former havinga flat apex. Further, as illustrated, concave-shaped wall 150 andconvex-shaped wall 160 are not equidistant along an axis orthogonal tothe longitudinal axis of the stent (not shown). Thus, in thisembodiment, the flat apex in concave-shaped wall 150 has been modifiedsuch that it comprises a pair of substantially rounded shoulders157,158.

With reference to FIG. 3, repeating pattern A is similar to the oneillustrated in FIG. 1. In FIG. 3, the flat apex of concave-shaped wall250 has been modified to provide a pair of rounded shoulders 257,258.Further, a strut 270 has been added to connect segment 254 ofconcave-shaped wall 250 and segment 264 of convex-shaped wall 260. Asillustrated, strut 270 is thinner in dimension that any of the segmentsmaking up concave-shaped wall 250 and convex-shaped wall 260. Thus,strut 270 may be considered as a relatively thin retention wire whichreconciles the need for retaining flexibility in the strut withmitigating lifting of rounded shoulders 257,258 when the stent isdelivered to the target body passageway through a relatively tortuousroute.

With reference to FIG. 4, repeating pattern A is similar to the oneillustrated in FIG. 1. In FIG. 4, the flat apex of concave-shaped wall350 has been modified to provide a pair of rounded shoulders 357,358.Further, a curved strut 370 has been added to connect segment 354 ofconcave-shaped wall 350 and segment 364 of convex-shaped wall 360.

With reference to FIG. 5, repeating pattern A is similar to the oneillustrated in FIG. 1. In FIG. 5, the flat apex of concave-shaped wall450 has been modified to provide a pair of rounded shoulders 457,458.Further, a curved strut 470 has been added to connect segment 454 ofconcave-shaped wall 450 and segment 464 of convex-shaped wall 460.Further, side walls 435,440 are also curved. As discussed above, sinceside walls 435,440 are bowed in opposite directions in adjacent rows ofrepeating pattern A and B, substantially diametric side walls inadjacent rows will function as the flexure means described above.

With reference to FIG. 6, repeating pattern A is similar to the oneillustrated in FIG. 1. In FIG. 6, concave-shaped wall 550 has beenmodified to have a flat apex 554 having a pair of rounded shoulders557,558 and convex-shaped wall 560 has been modified also to have a flatapex 564 having a pair of rounded shoulders 567,568. Further, a curvedstrut 570 has been added to connect flat apex 554 of concave-shaped wall550 and flat apex 564 of convex-shaped wall 560. Further, side walls535,540 are also curved.

With reference to FIG. 7, repeating pattern A is similar to the oneillustrated in FIG. 1. In FIG. 7, concave-shaped wall 650 has beenmodified to have a flat apex 654 having a pair of rounded shoulders657,658 and convex-shaped wall 660 has been modified also to have a flatapex 664 having a pair of rounded shoulders 667,668. Further, a curvedstrut 670 has been added to connect flat apex 654 of concave-shaped wall650 and flat apex 664 of convex-shaped wall 660. Further, side walls635,640 are also curved. Still further, walls 661,662 which connect flatapex 664 to side walls 635,640, respectively, and walls 651,652 whichconnect flat apex 654 to side walls 635,640, respectively, are eachcurved. It is believed that this design even further enhances thelateral flexibility of the stent.

With reference to FIG. 8, repeating pattern A is similar to the oneillustrated in FIG. 1. In FIG. 7, concave-shaped wall 750 has beenmodified to have a flat apex 754 having a pair of rounded shoulders757,758 and convex-shaped wall 760 has been modified also to have a flatapex 764 having a pair of rounded shoulders 767,768. Further, a strut770 has been added to connect flat apex 754 of concave-shaped wall 750and flax apex 764 of convex-shaped wall 760. Further, side walls 735,740have been modified to include a sinusoidal (or S-shaped) portion736,741, respectively, adjacent convex-shaped wall 760. Further, strut770 has been modified to include a sinusoidal (or S-shaped) portion 771adjacent flat apex of concave-shaped wall 750. This design even furtherenhances the lateral flexibility of the stent.

With reference to FIG. 9, repeating pattern A is similar to the oneillustrated in FIG. 1. In FIG. 9, concave-shaped wall 850 has beenmodified to have a flat apex 854 having a pair of rounded shoulders857,858. Further, side walls 835,840 have been modified to include apair of sinusoidal (or S-shaped) portions 836,841, respectively,adjacent convex-shaped wall 860. This design further enhances thelateral flexibility of the stent illustrated in FIG. 2. It should benoted that each sinusoidal (or S-shaped) portion 836,841 in FIG. 9comprises a pair of adjoined curved sections wherein each curved sectionhas an arc of greater than 180°—another way to conceptualize this is apair of link omega-shaped sections (cf. with the curved sections ofsinusoidal (or S-shaped) portions 736,741,771 in FIG. 8).

With reference to FIG. 10, repeating pattern A is similar to the oneillustrated in FIG. 1. In FIG. 10, concave-shaped wall 950 has beenmodified to have a flat apex 954 having a pair of rounded shoulders957,958. Further, a strut 970 has been added to connect flat-apex 954 ofconcave-shaped wall 950 and segment 964 of convex-shaped wall 960.Further, side walls 935,940 have been modified to include a pair ofsinusoidal (or S-shaped) portions 936,941, respectively, adjacentconvex-shaped wall 960. Further, strut 970 has been modified to includesinusoidal (or S-shaped) portion 971 adjacent flat apex ofconcave-shaped wall 950. It should be noted that each sinusoidal (orS-shaped) portion 936,941,971 in FIG. 10 comprises a pair of adjoinedcurved sections wherein each curved section has an arc of greater than180°. Further, the curved sections in sinusoidal (or S-shaped) portions936,941 are of the same size, whereas the curved sections in sinusoidal(or S-shaped) portion 971 are of different size. A distinct advantage ofthe interspersion of sinusoidal (or S-shaped) portions 936,941 andsinusoidal (or S-shaped) portion 971 is that substantially uniformradial expansion of all segments in this stent will occur withoutspecific regard to the expansion forces generated by the balloon orother means used to deploy the stent. Further, this design minimizes theforce (e.g. pressure from a balloon) required to expand the stent. Stillfurther, this design enhances the lateral flexibility of the stent.

As will be apparent to those of skill in the art, sinusoidal (orS-shaped) portion 971 is offset with respect to sinusoidal (or S-shaped)portions 936,941 in a panel horizontal to the longitudinal axis ofrepeating pattern A. The offset nature of these sinusoidal (or S-shaped)portions serves to increase the bending points in the stent allowing thestent to bend while avoiding buckling thereof. Thus, the stageddistribution of the sinusoidal (or S-shaped) portions over a largeportion of the surface area of the stent serves to improve theflexibility of the stent.

The advantages of the various alternate embodiments illustrated in FIGS.2-10 are discussed hereinabove.

As discussed above, the use of flexure means, such as the sinusoidal (orS-shaped) portions in the design of the stents illustrated in FIGS.8-10, in the longitudinal struts in the stent design provides the addedbenefit of improved flexibility of the stent in the unexpanded state.Specifically, during flexure of the stent, provision of such a featureallows the inner stent surface adjacent the bend to compress whileconcurrently allowing the outer stent surface adjacent the bend toextend, all while maintain substantially intact the integral strength ofstent and avoiding buckling of the stent.

Accordingly the provision of such flexure means in the longitudinalstruts of an otherwise general stent design is another feature ofinvention. With reference to FIGS. 12a-12 i there are illustratedvarious alternatives of bowed lateral sections which can be used inplace of sinusoidal (or S-shaped) portions 736,741,771 in FIG. 8,sinusoidal (or S-shaped) portions 836,841 in FIG. 9 and sinusoidal (orS-shaped) portions 936,941,971 in FIG. 10. Thus, the flexure meansillustrated in FIG. 12a may be considered to be an asymmetric zig-zagwhereas that illustrated in FIG. 12b may be considered to be a symmetriczig-zag and that illustrated in FIG. 12c may be considered to be an inline symmetric double peak. The flexure means illustrated in FIG. 12dmay be considered to be a single omega, whereas that illustrated in FIG.12e may be considered to be an inline (and unlinked) double omega andthat illustrated in FIG. 12f may be considered to be an opposed (andunlinked) double omega. The flexure means illustrated in FIG. 12g may beconsidered to be an opposed omega (facilitates extension)/U-joint(facilitates compression). Still further the flexure means illustratedin FIG. 12h may be considered to be a rail flex whereas that illustratedin FIG. 12i may be considered to be an opposed rail flex. Other specificdesigns which are with the spirit and scope of the present inventionwill be apparent to those of skill in the art.

Those of skill in the art will recognize that it is possible to combinevarious of the alternate embodiments illustrated in FIGS. 2-10 and 12 toderive further designs which are still within the spirit and scope ofthe present invention. Specifically, a preferred embodiment of thepresent invention involves combining various of the repeating patternsillustrated in FIGS. 2-10 to achieve a stent with relatively flexibleand rigid regions, for example, as follows:

F-R

F-R-F

R-F-R

wherein F is a relatively flexible region and R is a relatively rigidregion. With reference to the embodiments illustrated in FIGS. 1-10, thetrackability of the stent through a tortuous pathway is enhanced fromthe design illustrated in FIG. 1 progressively through to the designillustrated in FIG. 10. For example, an embodiment of the invention is astent comprising a first section incorporating the design of FIG. 10 anda second section incorporating the design of FIG. 9. It is believed thatsuch a multi-sectional design provides a very desirable combination oflateral flexibility (primarily from the design of FIG. 9) withpost-expansion radial rigidity (primarily from the design of FIG. 10).

Another technique by which the relative flexibility/rigidity may bevaried along the length of the stent involves varying the thickness ofthe segments making up the polygon discussed hereinabove. Specifically,the thickness of the segments may be varied in the range of from about0.0015 to about 0.0045 inches, preferably from about 0.0020 to about0.0040 inches. The lower the thickness in this range, the more flexiblethe resulting stent design. Conversely, the higher the thickness in thisrange, the less flexible the resulting stent design. Thus, by judiciousselection of segment thickness, the relative flexibility/rigidity of thestent may be varied along its length.

The provision of a stent with a variable relative flexibility/rigidityalong its length is believed to be novel, especially a stent comprisinga single relatively flexible portion and a single relatively rigidportion (i.e. the F-R embodiment discussed above). Such a stent wouldfind immediate use in a number of applications. For, example, such astent would very desirable for implantation in an ostial stenosis (thesetypically occur in coronary arteries, vein grafts and renal arteries).In this regard, an ostial stenosis is illustrated in FIG. 11 thereof.Thus, there is illustrated a right coronary cusp 105, a right coronaryartery 110 and an ostial segment 115 of right coronary artery 110. Asfurther illustrated a stenosis 120 presents a narrowing of ostialsegment 115. Ideally, a stent capable of implantation into such anostial stenosis must be of sufficient rigidity after expansion to resistthe elastic recoil of the ostial blockage (Region Y in FIG. 11).However, a stent of such sufficient rigidity will be deficient since itwill either: (i) be retarded in its advance along the artery due to thesharp bend in the right coronary artery (Region X in FIG. 11); or (ii)traverse the sharp bend in the right coronary artery but subsequentlystraighten Region X of right coronary artery 110 thereby increasing thelikelihood of tearing the artery. Conversely, a stent of sufficientlyflexibility to traverse the sharp bend in the right coronary artery(Region X in FIG. 11) is susceptible to recoil in the ostial rightcoronary artery (Region Y in FIG. 11). Accordingly, to the knowledge ofthe Applicant, there is no known effective manner by which a stent maybe used to treat an ostial stenosis of the type illustrated in FIG. 11.It is believed that a stent having variable relativerigidity/flexibility along its length as discussed above is a novelmeans by which an ostial stenosis may be treated. FIG. 11 also serves toillustrated the substantially complementary extension and compression oflongitudinal members in Region X of the right coronary artery.

The manner by which the present stent is manufactured is notparticularly restricted. Preferably, the stent is produced by lasercutting techniques applied to a tubular starting material. Thus, thestarting material could be a thin tube of a metal or alloy (non-limitingexamples include stainless steel, titanium, tantalum, nitinol, Elgiloy,NP35N and mixtures thereof) which would then have sections thereof cutout to leave repeating pattern A discussed above. Thus, the preferreddesign of the present stent is one of a tubular wall which is distinctfrom prior art wire mesh designs wherein wire is conformed to thedesired shape and welded in place. The preferred tubular wall design ofthe present stent facilitates production and improves quality control byavoiding the use of welds and, instead, utilizing specific cuttingtechniques.

Preferably, the stent is coated with a solution of 1:2 (mole) copolymerof (methacryloyloxy ethyl)-2-(trimethylanmronium ethyl) phosphate innersalt with lauryl methacrylate in ethanol (as described in Example 2 ofInternational patent application WO-A-93/01221) as follows. Thenon-expanded stent may be placed in a tube having a slightly largerdiameter than the stent. The tube may then be filled with coatingsolution and the solution allowed to drain steadily from the tube toform a completely coated stent. Immediately thereafter a stream of warmair or nitrogen may be directed through the tube at a linear velocity of0.1.5 m/s at room temperature to 50° C. for a period of 30 seconds to 5minutes to dry the coating by evaporation of the ethanol solvent.

As an alternative or in addition (on top or underneath) to this coating,a cross-linkable coating may be used consisting of a polymer of 23 mole% (methacryloyloxy ethyl)-2-(trimethylammonium ethyl) phosphate innersalt, 47 mole % lauryl methacrylate, 5 mole % γtrimethoxysilylpropylmethacrylate and 25 mole % of γhydroxypropyl methacrylate. This may beapplied to the sent by the above described technique from a 5 mg/mlethanoic solution. The solution may be dried as described above and thencured by heating at 70 to 75° C. for a period of at least about 1 hour,for instance overnight. This curing generally results in substantiallycomplete reaction of the methoxy silyl groups, either with othermethoxylsily groups or with hydroxy groups derived from thehydroxypropyl methacrylate monomer, driving off methanol. In onepreferred embodiment the crosslinkable coating is applied to the clearedstent, cured and then a further coating of the lauryl methacrylatecopolymer described above is applied.

The coated stent may be sterilised by ethylene oxide, gamma radiation orelectron beam and subsequently mounted onto a balloon catheter fordelivery.

Stent 10 can be implanted using a conventional system wherein aguidewire, catheter and balloon can be used to position and expand thestent. Implantation of mono-tubular stents such as stent 10 isconventional and within the purview of a person skilled in the art. See,for example, any one of U.S. Pat. Nos. 4,733,665, 4,739,762, 5,035,706,5,037,392, 5,102,417, 5,147,385, 5,282,824, 5,316,023 and any of thereferences cited therein or any of the references cited hereinabove.When the present stent is constructed as a bifurcated stent, it may beimplanted using the procedure outlined in the '997 patent applicationincorporated herein by reference. Such a bifurcated stent may bemanufactured, inter alia, by any of the methods disclosed in theCanadian patent application number 2,175,720 filed in Applicant's nameon May 3, 1996, the contents of which are hereby incorporated byreference.

It will be apparent to those of skill in the art that implantation ofstent 10 can be accomplished by various other means. For example, it iscontemplated that the stent can be made of a suitable material whichwill expand when a certain temperature is reached. In this embodiment,the material may be a metal alloy (e.g. nitinol) capable ofself-expansion at a temperature of at least about 30° C., preferably inthe range of from about 30° to about 40° C. In this embodiment, thestent could be implanted using a conventional catheter and the radiallyoutward force exerted on the stent would be generated within the stentitself. Further, stent 10 can be designed to expand upon the applicationof mechanical forces other than those applied by a balloon/catheter. Forexample, it is possible to implant stent 10 using a catheter equippedwith a resisting sleeve or retaining membrane which may then be removedwith the catheter once the stent is in position thereby allowing thestent to expand. Thus, in this example, the stent would be resilientlycompressed and would self-expanded once the compressive force (i.e.provided by the sleeve or membrane) is removed.

As will be appreciated by those of skill in the art, repeating pattern Ahas been described hereinabove and illustrated in FIG. 1 in respect of amonotubular stent. Repeating pattern A and all of the features relatingthereto illustrated in and described with reference to FIGS. 1-10(including modification to include the flexure means illustrated inFIGS. 12a-12 i) is equally applicable to a bifurcated stent such as theone described and illustrated in the '997 application discussedhereinabove, the contents of which are hereby incorporated by reference.

While this invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications of the illustrative embodiments,as well as other embodiments of the invention, will be apparent topersons skilled in the art upon reference to this description. It istherefore contemplated that the appended claims will cover any suchmodifications or embodiments.

What is claimed is:
 1. A stent comprising: a plurality ofradially-expandable circumferential struts; and a plurality oflongitudinal struts, each longitudinal strut having a curved flex memberwhich is spaced apart from any circumferential strut, the curved flexmember comprising, in two dimensions, a first curved section and asecond curved section; wherein the first curved section and the secondcurved section are of a different size.
 2. The stent defined in claim 1,wherein the first curved section and the second curved section are onopposite sides of a longitudinal axis of the stent.
 3. The stent definedin claim 1, wherein the first curved section comprises a U-shapedsection.
 4. The stent defined in claim 1, wherein the second curvedsection comprises a U-shaped section.
 5. The stent defined in claim 1,wherein the first curved section and the second curved section eachcomprise a U-shaped section.
 6. The stent defined in claim 5, whereinsaid first U-shaped section and said second U-shaped section areinterconnected.
 7. The stent defined in claim 1, further comprising amedicinal coating disposed thereon.
 8. A stent system comprising aballoon catheter having an expandable portion, the expandable portionhaving disposed thereon the stent defined in claim
 1. 9. A stentcomprising: a plurality of radially-expandable circumferential struts;and a plurality of longitudinal struts, each longitudinal strut having acurved flex member which is spaced apart from any circumferential strut,the curved flex member comprising a first curved section and a secondcurved section; wherein the first curved section and the second curvedsection are of a different size, wherein the first curved section andthe second curved section each comprise a U-shaped section, and whereinsaid first U-shaped section and said second U-shaped section comprise apair of straight sections which are: (i) parallel to each other, and(ii) substantially orthogonal to a longitudinal axis of the stent.
 10. Astent comprising: a plurality of radially-expandable circumferentialstruts; and a plurality of longitudinal struts, each longitudinal struthaving a curved flex member which is spaced apart from anycircumferential strut, the curved flex member comprising, in twodimensions, a first curved section and a second curved section; whereinthe first curved section and the second curved section are of adifferent size, at least one of the plurality of radially-expandablecircumferential struts having a thickness thereof which varies in therange of from about 0.0015 to about 0.0045 inches.
 11. A stentcomprising: a plurality of radially-expandable circumferential struts;and a plurality of longitudinal struts, each longitudinal strut having acurved flex member which is spaced apart from any circumferential strut,the curved flex member comprising, in two dimensions, a first curvedsection having arc of greater than 180°.
 12. The stent defined in claim11, wherein said curved flex member comprises a second curved sectionhaving an arc of greater than 180°.
 13. The stent defined in claim 12,wherein the first curved section and the second curved section are onopposite sides of a longitudinal axis of the stent.
 14. The stentdefined in claim 12, wherein the first curved section and the secondcurved section have substantially the same shape.
 15. The stent definedin claim 12, wherein the first curved section and the second curvedsection have substantially the same size.
 16. The stent defined in claim12, wherein the first curved section and the second curved havesubstantially the same size and the same shape.
 17. The stent defined inclaim 12, wherein the first curved section and the second curved sectionare interconnected.
 18. The stent defined in claim 11, furthercomprising a medicinal coating disposed thereon.
 19. A stent systemcomprising a balloon catheter having an expandable portion, theexpandable portion having disposed thereon the stent defined in claim11.
 20. A stent comprising: a plurality of radially-expandablecircumferential struts; and a plurality of longitudinal struts, eachlongitudinal strut having a curved flex member which is spaced apartfrom any circumferential strut, the curved flex member comprising, intwo dimensions, a first curved section having arc of greater than 180°,at least one of the plurality of radially-expandable circumferentialstruts having a thickness thereof which varies in the range of fromabout 0.0015 to about 0.0045 inches.
 21. The stent defined in claim 20,wherein said plurality of radially-expandable circumferential struts andsaid plurality of longitudinal struts are formed in a porous tubularwall.
 22. The stent defined in claim 20, wherein said plurality oflongitudinal struts comprises plural flex members disposed in at leastone row of longitudinal struts.